Leading the Charge

March 19, 2013

Jongyoon Han is engineering ion imbalances to clean water and activate neuroprosthetics.

Jongyoon Han; Associate Professor, Electrical Engineering and Computer Science/Biological EngineeringJongyoon Han is a self-described daydreamer. He's naturally drawn to thinking of new ways to perform any activity--whether finding a new route to his vacation spot or new applications of fundamental science. Today, Han is using his innate curiosity and proven facility in engineering, physics, and biology to develop new water desalinization and purification technology and new neuroprosthetics--two seemingly unrelated research areas to the uninitiated. But Han is thoroughly familiar with the fundamental physics underlying these applications--the science of ion concentration polarization.

Those working in selective membranes have known about the ion concentration polarization phenomenon for some time. By definition membranes pass one type of material or molecule while blocking another. A unique type of membrane, known as ion selective membranes, repels or blocks the passage of positive ions, for example. These membranes have found use in engineering fuel cells.

When an electric field passes across an ion selective membrane, ions are driven in both directions. The membrane in the middle blocks one type of ion while passing the other in the process creating a charge imbalance. Explains Han, "If you create a group of positive ions on one side and negative ions on the other side of the membrane there is a strong electrostatic interaction between them creating the condition of ion concentration polarization." But when ion concentration changes so does the entire electric field distribution which can induce strong fluid motions around it.

With a background in physics, Han joined the MIT faculty in 2002 in the Department of Electrical Engineering and Computer Science. He later joined the newly created Department of Biological Engineering where his work on ion concentration polarization has progressed rapidly, and today he is also Head of the Micro/Nanofluidic BioMEMS Group at the MIT Research Lab of Electronics. Since 2005, Han has homed in on the science of ion concentration polarization to find practical solutions to two of today's scientific challenges.

Water Desalinization and Purification

Han's first attempt at engineering ion concentration polarization led to creating a biosensing device that concentrated biomolecules in one location. Instead of having a low concentration biomolecule sample, this device concentrated these biomolecules in a small region making it easier to detect them.

Later, Han realized that is was not just moving the biomolecules but the ions itself, or the salt contained in the system. From there sprang the idea of moving the salt in the water to actually desalinate it. The team successfully produced a technology and published their first desalinization paper in 2010.

"It is the same principle but using it for different industry," Han says. "Because you can move the ions away or draw them in, you can use the phenomena to push the ions around and desalinate the water, even from the sea water to the fresh water level."

One of the benefits of ion concentration polarization technology is that not only are salts removed from the water but it also clears larger charged colloid particles like cells, bacteria, and proteins. "It is one of the very clear benefits of this technology," he explains. "In a single same step you can actually remove all the salt and bacteria from the cells together."

To commercialize the technology, Han and colleagues are in the process of launching a small start-up company for small-scale household or personal use water purification. The team is aiming to produce the clarified water with "good power efficiency" that may include solar panel technology instead of using larger amounts of electricity. The other necessary metric is to build a portable technology that can be used anywhere, including in disaster-stricken regions. "You can bring the device to the problem and apply it without the need for electricity or infrastructure support."

Han realizes that the technology has potential to be competitive for large-scale water desalinization and purification production but it has yet to be demonstrated on that scale. To do so, he is seeking to raise government or industry support to fund the necessary engineering work to bring this new desalinization idea to the larger markets.

Neuroprosthetics

In 2010, Han thought of applying ion concentration polarization science in the context of nerve cells. The nerve is a circuit that conducts electrical impulses based on ion current in and out of the membrane. The nerve cell naturally maintains a certain ion concentration imbalance between the inside and outside of the cell. When a signal is received, the nerve opens up the ion channel protein allowing ions to flow into the nerve cell.

"We understood that this process is critically dependent on the concentration of different ions around the nerve cell," Han explains. For more than 100 years scientists have known that decreasing the calcium concentration around the nerve causes it to become hypersensitive. The nerve can then be excited and triggered with lower amounts of current.

"That is where we got the idea that if we deplete the calcium concentration around the nerve and make it more hypersensitive then we could make better prosthetics," Han recalls. The goal of neuroprosthetics is to artificially excite often-damaged nerves in the area to allow muscle activation. Today, that is achieved by positioning electrical current into the nerve.

Working with clinical collaborators from Beth Israel Hospital, Han's team published their first paper related to neuroengineered prosthetics in 2011. The paper focused on the use of a new calcium-selective ion membrane. The team designed a metal electrode coated with this membrane material. "It depletes the calcium ions around the nerve so that when we excite the nerve we clearly see the decrease of the threshold current," he explains.

"If we can control the ion concentration of that location, you can make the nerve locally hypersensitive so you don't need to apply higher amount of current." The benefits could make the use of prosthetics potentially more comfortable. Since the entire area conducts electricity, applying higher levels may trigger another nerve, including a sensory nerve that will register pain or heat. "I think we can make a clear impact on those parasitic activation issues because we can potentially lower the amount of current significantly," Han concludes.

Putting "Crazy Ideas" to Work

Regardless of what he studies, Han's research modus operandi is to begin with some mundane, obscure physics phenomenon. "You try to understand the physics behind it and then you realize that there are some things you can do with this phenomenon. Maybe you can make a new device or a different system to capitalize on this unique phenomenon," he explains. "For example, when I see a neuroprosthetic I don't see the prosthetic. I think about what happens between the electrode and the cell."

Han partly credits the MIT culture with focusing his "crazy ideas" into research projects. "MIT places so much emphasis on the practical use of science, engineering, and technologies," he says. "Whenever I see other people present their work, they all talk about what it might be used for. That is the culture of this place and the practically-minded scientist."

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